What is the role of interfaces in creating maintainable code?

1 What are interfaces?

An interface is a contract that defines the methods and properties that a class or a struct must implement. An interface does not provide any implementation details or state; it only specifies what the class or struct can do. For example, you can define an interface called IShape that has a method called GetArea() and a property called Color . Any class or struct that implements this interface must provide its own logic for calculating the area and storing the color.

2 Why use interfaces?

One of the main benefits of using interfaces is that they enable interface inheritance, which is a form of code reuse. Interface inheritance allows you to define a hierarchy of interfaces that inherit from each other, and then implement them in different classes or structs. For example, you can define an interface called ICircle that inherits from IShape and adds a property called Radius . Then, you can create a class called Circle that implements ICircle , and another class called Cylinder that also implements ICircle and adds a property called Height . By using interface inheritance, you can avoid duplicating code and ensure consistency among different types.

4 How do interfaces help with testing?

A final benefit of using interfaces is that they help with testing, which is the process of verifying the correctness and quality of your code. Testing is easier when you use interfaces, because you can create mock objects that implement the same interface as the real objects that you want to test. A mock object is a fake object that mimics the behavior of the real object, but with predefined values and responses. For example, if you want to test a class called ShapeCalculator that uses an IShape object to perform some calculations, you can create a mock object that implements IShape and returns a fixed value for the GetArea() method. Then, you can pass the mock object to the ShapeCalculator class and check if it produces the expected results. By using mock objects, you can isolate the code that you want to test and avoid dependencies on external factors.

5 What are some best practices for using interfaces?

Now that you know what interfaces are and how they can help you create maintainable code, here are some best practices for using them effectively. It's important to use descriptive and consistent names for your interfaces, following the naming conventions of your programming language. For example, in C#, it is common to prefix interface names with I , such as IShape or ICircle . Interfaces should be used to define the behavior and functionality of your types, not their data or state. For instance, instead of creating an interface called IPerson with properties like Name or Age , create an interface called IGreetable with a method like Greet() . Interfaces can also be used to decouple code from specific implementations and dependencies. Moreover, they can support multiple inheritance and composition, which are design patterns that let you combine the features and behavior of different types. Instead of creating a class that inherits from multiple classes, create an interface that inherits from multiple interfaces, and then implement it in a class that uses composition to delegate the functionality to other objects.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?